The present invention relates to an ink jet recording apparatus that performs recording by ejecting ink toward a recording medium. More specifically, the present invention relates to an ink jet recording apparatus that performs recording by supplying ink to an ejection head by a static pressure method and by ejecting the ink from the ejection head.
As an ink jet recording apparatus that performs recording by ejecting ink toward a recording medium, there is provided, for example, an electrostatic ink jet recording system in which an electrostatic force is caused to act on ink to eject ink droplets. As one type of the electrostatic ink jet recording system, there is known an ink jet recording apparatus using ink obtained by dispersing a charged fine particle component containing colorant and resin (hereinafter referred to as “colorant particles”) in an insulative carrier liquid (dispersion medium) and performs recording with a method with which an image is recorded onto a recording medium in an on-demand manner through control of ejection of the ink in which an electrostatic force is caused to act on the ink by applying voltages (drive voltages) to ejection electrodes of an ink jet head in accordance with image data.
In the electrostatic ink jet recording that uses the ink containing the colorant particles, the electrostatic force is caused to act on the ink at ink ejection portions (and near the ejection portions) by applying drive voltages to the ejection electrodes formed in correspondence with the ejection portions under a state in which the recording medium is charged to a bias voltage and is set to face the ink jet head, for instance.
Through the application of the electrostatic force, the colorant particles migrate and gather at the ejection portions (that is, the ink is concentrated at the ejection portions) and are ejected as ink droplets.
As a method of supplying the ink to each ejection portion in the electrostatic ink jetting system, for instance, it is possible to use a method with which the ink is circulated through a predetermined circulation path in which the ink is supplied from a tank reserving the ink to the ink jet head, the ink is caused to flow through a predetermined ink flow path communicating with each ejection portion in the ink jet head, and the ink not ejected and passed through the ink flow path is returned from the ink jet head to the tank.
For instance, JP 10-244690 A discloses an ink jet recording apparatus as shown in FIG. 6 which records an image on a recording medium P by ejecting ink containing colorant particles from an electrostatic ink jet head (hereinafter referred to as “recording head”) 200, and includes a circulation, system that supplies the ink from a tank 202 reserving the ink to a tank 206 with a pump 204, supplies the ink from the tank 206 to the recording head 200 through a gravity drop under a water head pressure, and returns the ink not ejected from the recording head 200 to the tank 202. In addition, the ink jet recording apparatus includes a tank 210 in which degraded ink is disposed, and a tank 214 in which new (unused) ink is reserved.
Also, in the ink jet recording apparatus, a degradation state of the circulated ink is detected. When a result of the detection indicates that the ink is degraded, the pump 204 is stopped, all of the ink in the tank 206 is recovered to the tank 202, and the degraded ink is then disposed in the tank 210 by opening a valve 208. When the tank 202 becomes empty, the new ink is supplied from the tank 214 to the tank 202 by opening a valve 212 and circulation is performed again.
Here, the ink jet recording apparatus disclosed in JP 10-244690 A is capable of supplying the ink at a constant pressure by supplying the ink from the tank 206 to the recording head (ejection head) 200 through a gravity drop under a water head pressure but has a possibility that coagulation solid matter is formed on an inner wall surface of the tank 206, a possibility that coagulation solid matter or the like is generated in the tank 206 due to evaporation of the ink at a gas-liquid interface at which the ink contacts the air, a possibility that dust will enter into the tank 206, and the like.
When foreign matter such as the dust and the coagulation solid matter is mixed into the ink and the ink containing the foreign matter is supplied to the recording head 200, ejection ports (nozzles) of the recording head may be clogged with the foreign matter and the ejection of ink droplets may become impossible.
Regarding this problem, the inventor of the present invention have found that in the ink jet recording apparatus that uses the sub-tank supplying the ink to the recording head with a static pressure method, by providing a filter that removes the foreign matter between the recording head and the sub-tank, it becomes possible to remove the foreign matter generated in the tank which supplies the ink to the recording head, and also prevent the recording head from being clogged with the foreign matter.
By providing the filter between the recording head and the sub-tank in the manner described above, it becomes possible to prevent the foreign matter from entering into the recording head. With this construction, however, there is a case where the ink remains in the filter even after the ink jet recording apparatus is temporarily stopped after use and the ink is extracted from the ink circulation system including the ink jet head and is returned to a main tank or the like. When the ink remains in the filter, depending on a static pressure applied to the recording head, the ink may become incapable of passing through the filter at the time of start of the ink supply to the recording head (at the time of start of the ink circulation) due to surface tension of the ink in the filter or the like and flow of the ink may be blocked by the filter. When the flow of the ink is blocked by the filter in the manner described above, there occurs a problem in that the ink is not supplied to the recording head and image recording becomes impossible.